This invention relates generally to tape recording and/or reproducing apparatus suitably for use as, for example, a video tape recorder (VTR).
In a VTR, a tape wound on supply and take-up reels is guided therebetween so as to be engageable by rotary heads associated with a guide drum for recording and reproducing video signals in tracks scanned on the tape which is wrapped about the periphery of the guide drum. Tape guides used for leading the tape to and from the guide drum are generally of the rotary-type or fixed-type. The rotary-type tape guides have the advantage of providing a relatively small resistance to the movement of the tape therepast. However, any irregularity in the bearing used for rotatably supporting the tape guide roller will cause corresponding irregularity in the running of the guided tape. Further, the tape has to run at right angles to the rotational axis of the rotary guide roller, as any deviation of the rotational axis from a precise perpendicular to the longitudinal direction of the tape will cause the tape to move transversely as it travels past the rotary guide roller. Such transverse movement of the tape will bring a longitudinal or side edge of the tape into bearing engagement with a flange provided on the guide roller, whereby the flange will crumple or otherwise damage the edge portion of the tape. Therefore, when rotary tape guides are used, the guides and the structures employed for mounting and positioning the same must be produced and assembled with very high precision, with the result that such guides are difficult and expensive to produce.
On the other hand, if fixed or non-rotatable guides are used to avoid the foregoing problems, the tape guides impose an undesirably large frictional resistance to the movement of the tape. In an attempt to minimize the frictional resistance to movement of the tape past non-rotatable guides, it has been proposed to employ a so-called "air guide", that is, a non-rotatable tape guide having perforations in its surface through which jets of air are propelled for establishing an air film between the tape and the guide surface. Although the described air guides provide a reduced frictional resistance to the movement of the tape, an air compressor or other source of air under pressure is required and introduces further complexity in the associated VTR.
In order to solve the foregoing problems, one of the inventors hereof has proposed, for example, as disclosed specifically in U.S. patent application Ser. No. 07/489,043, filed Mar. 5, 1990, and having a common assignee herewith, a non-rotary tape guide device in which a guide element is subjected to ultrasonic vibration so as to impose small frictional resistance to the travel of the tape while guiding the tape in a stable manner without the danger of inflicting damage thereto. Other ultrasonic tape guide elements are described in commonly owned U.S. application Ser. No. 07/841,045, filed Feb. 25, 1992, now U.S. Pat. No. 5,263,624 and U.S. application Ser. No. 07/856,174, filed Mar. 23, 1992, now U.S. Pat. No. 5,224,643.
Although it may seem relatively simple to provide the necessary ultrasonic energy for effecting vibration of the tape guide, there are problems associated therewith. More specifically, the frequency of the ultrasonic energy applied to the guide element for effecting the ultrasonic vibration thereof should be a resonant frequency of the guide element However, such resonant frequency changes with temperature. Further, the amplitude or power of the ultrasonic energy required for effecting ultrasonic vibration of the guide element so as to achieve the desired reduction of the frictional resistance to movement of the guided tape varies with tape speed. In fact, when the tape runs at very high speeds, for example, as in the fast-forward or rewind mode, an air film is drawn between the surface of the guide element and the tape so that the frictional resistance to movement of the tape is sufficiently reduced by such air film and ultrasonic vibration of the guide element is not then required. Accordingly, generation of the ultrasonic energy for vibrating the guide element at a constant power level results in wasteful power consumption.